1. Field of the Invention
The present invention relates to a disk array apparatus which is incorporated in a RAID (Redundant Array of Inexpensive Disks) employing optical disks as portable media and which can access a plurality of optical disks in parallel at high speed and manage the files recorded in the disks with high efficiency.
2. Description of the Related Art
In recent years, a data array apparatus has been commercialized as an apparatus which ensures high-speed data transfer and which hardly breaks down. A disk array apparatus employing a hard disk drive is known as a fixed memory apparatus which is called a RAID (Redundant Arrays of Inexpensive Disks) system (refer to 1988 ACM Association For Computing Machinery).
In this type of disk array apparatus, data is distributively recorded in a plurality of hard disks, except in the hard disks in the form of mirrors, in units of one bit or one byte (RAID2, RAID3) or in units of one sector (RAID4, RAID5), so that data can be written or read by the hard disk drives in parallel.
The disk array apparatus enables a number of hard disks to be accessed in parallel, so that a high-speed operation is ensured. In addition, the disk array apparatus comprises a hard disk for storing redundant data, and data can be generated even if one of the hard disk drives breaks down. Therefore, the disk array apparatus is improved in reliability.
The conventional art will be described with reference to FIG. 1.
FIG. 1 is a block diagram of a conventional disk array apparatus employing hard disk drives. The disk array apparatus comprises: a host interface section 1 for performing interface control with reference to a host computer; CPU 2 for controlling the entire disk array apparatus; a memory 3 for temporarily storing the program codes or data of CPU 2, the communication data exchanged with reference to the host apparatus, and the data to be stored in a hard disk; file management means 5 for managing the files stored in the disk array apparatus; data transfer means 4 for transferring data between the storage medium and the memory 3 and between the memory 3 and the host computer; disk controllers 6a, 6b, 6c, 6d, and 6e for controlling the hard disk drives; and ten hard disk drives 7a, 7b, 7c, 7d, and 7e.
Of the ten hard disk drives 7a, 7b, 7c, 7d, 7e, 8a, 8b, 8c, 8d, and 8e, those denoted by 7a, 7b, 7c, 7d, and 7e constitute Group 1 and those denoted by 8a, 8b, 8c, 8d, and 8e constitute Group 2.
Two of the hard disk drives are connected to each of the disk controllers 6a, 6b, 6c, 6d, and 6e, respectively. All hard disk drives can be accessed without changing the connections among them, by selectively designating the hard disk drives.
The conventional art shown in FIG. 2 is a RAID4 mode, and parity data is stored in the hard disk drives 7e and 8e that are connected to disk controller 6e, and ordinary data is stored in the other hard disks in a distributed manner. Let it be assumed that data is stored in a distributed manner in units of 16 KB in the conventional art shown in FIG. 2. In this case, file "Text1" having a size of 64 KB is stored in a distributed manner such that the first 16 KB data is stored in hard disk drive 7a, the next 16 KB data is stored in hard disk drive 7b at an area of the same address, the next 16 KB data is stored in hard disk drive 7c at an area of the same address, and the last 16 KB data is stored in hard disk drive 7d at an area of the same address.
Let it be assumed that an access request for file "Text1" stored in the hard disk drives of Group 1 and an access request for file "Text3" stored in the hard disk drives of Group 2 are made simultaneously. In this case, the two files "Text1" and "Text3" cannot be accessed simultaneously since the hard disks of Group 1 in which file "Text1" is stored and the hard disks of Group 2 in which file "Text3" is stored are connected to the same disk controllers 6a, 6b, 6c, and 6d. File "Text3" is accessed immediately after file "Text1" is accessed.
The hard disks 8a, 8b, 8c, and 8d in which file "Text3" is stored and the hard disks 7a, 7b, 7c, and 7d in which file "Text3" is stored are different, but these files can be accessed by selectively designating the hard disks in which they are stored, and the connections among the hard disks need not be changed at the time of access.
Where optical disks are employed as portable media, however, files stored in hard disks of different groups cannot be accessed by merely designating the hard disks, and all optical disks have to be replaced, resulting in a long operation time.
In a parallel system which is not a RAID system employing optical disks, no consideration is given to a library function which makes use of the merits of portable media, and data is recorded in a distributed manner only.
In disk array apparatuses, including the conventional art mentioned above, a number of optical disks are recorded in a distributed manner in units of one bit or one byte (RAID2, RAID3) or in units of one sector (RAID4, RAID5), and data is written or read by the hard disk drives in parallel. All data are distributively stored in the optical disks and are grouped in units of a certain number of optical disks. In a disk array apparatus employing portable optical disks, therefore, the grouped optical disks must be loaded in the respective optical disk drives. If the optical disks must be replaced with others, a very long time is required for accessing a target file stored in the optical disks.